Apparatus for manufacturing long, slender lamina stacks from nonuniform laminae

ABSTRACT

A method of manufacturing an elongate stack of interlocked laminae in a die assembly. The method includes the steps of stamping a first lamina having generally opposed first and second edges in the strip stock material, stamping at least one first interlock means for engaging another lamina in the first lamina, separating the first lamina from the strip stock material, placing the first lamina into the choke passageway, the first and second edges of the first lamina frictionally engaging the choke passageway, stamping a second lamina having first and second elongate edges in the strip stock material, stamping at least one second interlock means for engaging another lamina in the second lamina, at least partially engaging the first and second interlocking means, separating the second lamina from the strip stock material, placing the second lamina into the choke passageway, and frictionally engaging the choke passageway along the first and second elongate edges of only one of the first and second laminae.

This is a Division of U.S. patent application Ser. No. 09/152,979, filedSep. 14, 1998, which is a Continuation-In-Part of U.S. patentapplication Ser. No. 08/963,795, filed Nov. 4, 1997, now U.S. Pat. No.6,131,268, issued Oct. 17, 2000, which is a Division of U.S. patentapplication Ser. No. 08/806,020, filed Feb. 24, 1997, now U.S. Pat. No.5,755,023, issued May 26, 1998, which is a Continuation-In-Part of U.S.patent application Ser. No. 08/658,595, filed Jun. 5, 1996, now U.S.Pat. No. 5,799,387, issued Sep. 1, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to laminated parts. Moreparticularly, the present invention relates to lamina stacks, andespecially long, slender lamina stacks, formed by stamping a pluralityof lamina layers from a sheet or strip of stock material and the methodsand apparatuses, i.e., progressive dies, used in the manufacture of suchlaminated parts.

2. Description of the Related Art

The manufacture of parts, e.g., stators and rotors for electric motors,employing stacked laminae is well known in the art. Typically, thelaminae are blanked from a continuous strip stock and then stacked andbound together to form the completed part. Progressive die assembliesfor producing laminated stacks, wherein a strip of lamina material isfed through a sequence of punching steps to progressively form thelaminae to the desired end configuration, are also well known.

It is also known to form, in the laminae, interlock tabs which extendbelow the generally planar lamina surface and engage slots formed in thenext lower lamina. In this manner, a plurality of laminae may be stampedfrom a single sheet of strip stock and formed into an interconnectedlamina stack in the die by means of interlocking tabs and slots. Morespecifically, to form an interconnected lamina stack each lamina, exceptthe bottom lamina of the stack, may have a plurality of arcuately spacedinterlock tabs (typically ranging from 3 to 8 circumferentially disposedtabs) depressed from the lamina lower surface adjacent to slots formedin the next lower lamina. Each interlock tab engages a correspondingslot in the next lower lamina of the stack, generally by the entirethickness of the tab. The bottom lamina of the stack may have theinterlock tabs blanked and removed to avoid interlocking the bottomlamina with the next lower lamina which forms the top lamina of theprevious stack. In rare instances the tab may lock as deeply as twolamina thicknesses, in which case two end laminae must be blanked.

Rotor laminae generally include a plurality of skewed conductor slotswhich are formed around the periphery of the rotor stack in arcuatelyspaced relation to one another. The conductor slots are arcuately spacedin an individual lamina in a fixed relationship to one another and, in arotor stack, are skewed relative to an adjacent lamina by rotationallyindexing the partially completed rotor stack with respect to the lastproduced lamina being attached thereto. Indexing involves rotating therotor stack and the last produced lamina relative to each other by apredetermined rotational increment so that, when the laminae arecombined in a stack, the rotor conductor bar slot defined by adjacentconductor slots are skewed or slanted relative to the stack axis. Statorstacks, on the other hand, include winding slots around the innerperiphery of the stack which extend parallel to the stack axis, withoutskew, and are shaped to receive the stator windings. In somecircumstances, however, it may be desired to build an “inside-out” motorwherein the outer lamina stack forms the rotor and would, thus, requireskewed slots.

Another system of forming a stack involves loosely stacking the laminaeas they are formed and blanked from the stock material in a progressivedie assembly. After all the laminae for a given stack are collected,they are shuttled to a pressing station and the laminae are pressedtogether to engage the interlock tabs and thereby form the lamina stack.Loosely stacking the laminae after they are blanked from strip stock hasseveral disadvantages; loose stacking and subsequent pressing does notas consistently lock adjacent laminae together; the required handlingslows production times; and the system lacks a means for automaticallycorrecting thickness inconsistencies of the stock material or creating adesired skew angle for the conductor slots. A similar process can beemployed without the use of interlocking features on the laminae.Assembly of the non-interlocked laminae requires the welding, keying orriveting (or pinning) of the laminae to interconnect the laminae in astack.

In response to these problems, an autorotation system for compensatingfor the nonuniform stock thickness was developed which both rotates andinterlocks the stacked laminae. This system compensates for variationsin lamina thickness while still properly skewing the conductor slots ofrotor laminae, as described in U.S. Pat. Nos. 4,619,028; 4,738,020;5,087,849 and 5,123,155, all assigned to the assignee of the presentinvention and the disclosures of which are incorporated herein byreference. In the system disclosed in the aforementioned patents, thechoke barrel or passageway holding the lamina stack may be automaticallyrotated before each lamina is blanked from the strip stock and thelamina's circumferentially disposed tabs are interlocked with the slotsof the uppermost lamina of the incomplete lamina stack within thebarrel. Alternatively, the choke may be automatically rotated with everyother press cycle, every third press cycle, and so on.

In the apparatus and method disclosed in the aforementioned patents, theindividual laminae are typically rotated through an angle of 180°.Although the laminae may be rotated through other angles, the angle mustbe at least 360°/(number of interlock tabs) so that the interlockingtabs and slots are properly aligned.

The above described improvements have been implemented with rotorlaminae and stator laminae which have identical outer perimeters whichenables their insertion into a choke barrel designed to hold a laminahaving the outer perimeter configuration of the laminae being stacked.Many of these improvements require the use of interlock tabs incombination with autorotation of a partially formed lamina stack.

Autorotation requires the use of a rotating choke barrel which firmlyholds the partially formed lamina stack in position as blanked laminaeare forced into engagement with the uppermost lamina of the stack. Thechoke barrel is typically configured to match the outer perimeter of theblanked lamina and may be slightly undersized, e.g., by 0.001 inch, sothat the laminae will be firmly held and accurately positioned withinthe choke barrel. The laminae, after they are located in the chokebarrel with an interference fit thereby provide back pressure orresistance which facilitates the entry of the interlock tabs of the nextlamina when it is pressed into the choke barrel.

In certain applications, however, it is desirable to have a laminastack, typically a stator core but also rotor cores in some situations,wherein some of the laminae have an outside perimeter which differs inshape and/or size from the remainder of the stack of laminae, i.e., thelaminae in the stack have a plurality of distinguishable configurations.For example, the stator core may incorporate a fastening feature, suchas a projecting flange, to provide a mounting surface which is integralwith the stator core, or the stator may incorporate a sealing feature toprovide a seal between the housing of the motor and the stator core formotors to be used in environments which include flammable vapors. Toincorporate such features, a fraction of the laminae in a stack aremanufactured with integral portions which provide such features.

Traditionally, the manner in which stator cores having a plurality ofouter perimeter configurations have been produced is to stamp thedifferently configured laminae in separate dies, i.e., each die providesonly a single lamina configuration. The plurality of dies produce looselaminae having the desired plurality of outer perimeter configurations.The laminae must then be manually assembled at a station where laminaeof the different outer perimeter configurations are placed in the propervertical stack arrangement and are pressed together to interlock thelaminae. Instead of using interlocking tabs, the laminae may also besecured together in some other conventional fashion such as by the useof clamps, pins, rivets or welds.

There are several drawbacks to this manner of manufacturing a laminacore having laminae with a plurality of outer perimeter configurations.For one, the manufacturing process is relatively expensive due to theuse of multiple dies and the large amount of labor and handling which isrequired. Further, production rates with this process tend to berelatively slow. Additionally, the process does not allow for theautomatic correction of lamina thickness inconsistencies.

Another problem with this method of manufacture is that it oftenproduces stator cores having winding slots with slight discontinuitiesand sharp edges. Because separate dies are used to form the differentlyconfigured laminae, the stator winding slots are punched by differentdies. Although similar in shape, the different punches cannot beprecisely identical and will generally have minor inconsistencies which,when the differing laminae are stacked, cause the slots in adjacentlaminae to misalign, thereby creating slight discontinuities and sharpedges in the winding slots at the points where the two differentlyconfigured laminae meet. These small discontinuities can scratch anddamage the winding coil wires which are inserted into the winding slots.

The discontinuities of the projections which define the winding slotsand interior surface of the stator core also reduce the efficiency ofthe electric motor or generator which is produced with the stator core.The efficiency of the motor or generator may be reduced if the gapbetween the stator core and rotor core is enlarged to account for thediscontinuities present on the interior surfaces of the stator corebecause the efficiency of the motor or generator is decreased as the gapincreases.

The manufacture of lamina stacks wherein individual laminae arecomprised of two or more discrete segments also presents significantmanufacturing difficulties. It is often impractical to manufacturelamina stacks wherein one or more of the laminae is formed by at leasttwo discrete lamina segments. Laminae comprised of a plurality ofdiscrete segments present difficulties in maintaining the properalignment between the various lamina segments which comprise theindividual lamina and between the lamina segments and the other laminaewhich comprise the remainder of the lamina stack.

Further, in certain applications it is desirable to have a stack ofinterlocked laminae which is long and slender, and which has across-sectional shape having lateral sides defined by the lamina outeredges which do not lie in a substantially common plane; such a stackdoes not provide a choke-engaging surface which extends substantiallyalong the vertical height of the stack. For example, it is desirable tohave an elongate, substantially cylindrically-shaped lamina stack, inwhich the first, bottommost lamina is narrower than the adjacent,overlying second lamina, which is narrower than the adjacent, overlyingthird lamina, and so on, with the middlemost lamina(e) defining thewidest portion of the substantially circular cross section andsubsequent adjacent, overlying laminae each having a reduced width ascompared to its adjacent lamina, thus forming a circular cross section,with each of the laminae of the cylindrically-shaped stackinterconnected. Notably, the stock material from which a lamina stackmay be produced according to the present invention is thin, and theindividual laminae stamped therefrom quite flexible. Because theindividual laminae of such a stack are long, thin and flexible, and mayalso have common choke-engaging edges forming a planar choke engagingsurface only at the longitudinal ends of the stack, the individuallaminae tend to inadequately support the stack in the choke opening orto cause the laminae to bow, rendering the above-described automaticinterlocking method unusable for manufacturing such stacks. Moreover,the above-described automatic interlocking method may also be difficultto use in producing interlocked stacks of laminae which are long, thinand flexible, but do have common choke-engaging edges forming a planarsurface at the lateral sides of the stack. Prior art manufacturingmethods for attaching the long, thin flexible laminae of these stackstogether include post-stacking welding, keying or riveting operations ora separate pressing operation for engaging the interlocking tabs, assuch prior art operations do not require the laminae to be firmly heldand accurately positioned within a choke opening.

What is needed is an apparatus and method for producing long, slender,interlocked stacks of flexible laminae in which the laminae areautomatically stamped, stacked and interlocked, the stacks havingcross-sectional shapes with side surfaces defined by the side edges ofthe laminae which may or may not commonly engage the adjacent chokesurfaces.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and method for manufacturingand automatically stacking a laminated stack which includes a laminacomprised of a plurality of discrete lamina segments and which mayinclude a plurality of differently configured laminae to thereby producelamina stacks which may include a plurality of slots and windowsseparating individual lamina segments. The present invention alsoprovides an apparatus and method for producing long, slender,interlocked lamina stacks wherein the individual laminae havecross-sectional shapes having sides which do not substantially lie in acommon plane.

An advantage of the present invention is that it permits the automaticstacking of a laminated stack which includes a lamina layer comprised ofdiscrete lamina segments thereby providing for the economicalmanufacture of lamina stacks which include a lamina or lamina layercomprising a plurality of discrete lamina segments. For example, linearmotors which require stator cores having slots on opposing sides of thecore for accommodating supports for an actuator disposed within thestator core may be economically manufactured by the present invention.The ability to automatically stack a lamina comprised of discrete laminasegments also permits the manufacture of a wide variety of laminatedstacks for applications beyond electrical motor and stator cores whichare uneconomical or impractical to manufacture using laminated stackswhich do not include laminae comprising discrete lamina segments.

Another advantage of the present invention is that the economicalmanufacture of laminated stacks comprising a lamina layer of discretelamina segments permits the manufacture of parts which were previouslystamped from a single thickness stock material. Manufacturing parts fromlaminae rather than from a single thickness stock material can eliminatesecondary operations. For example, notches can be placed in selectedlaminae prior to stacking to thereby form a notch or opening in theoutside edge or wall of the laminated stack which does not extend theentire height of the stack and which, if formed in a part stamped from asingle thickness of stock material, would require a secondary machiningoperation after stamping.

Yet another advantage of the present invention is that it permits theautomatic stacking of a laminated stack having a plurality ofdistinguishable outer perimeter configurations. The need to manuallyhandle and stack laminae to form a lamina stack having a plurality ofouter perimeter configurations and/or a lamina layer comprising aplurality of discrete segments is thereby eliminated. The conveyor,pressing and stack securing equipment used in the traditional manualassembly method are also eliminated by the present invention.

Yet another advantage of the present invention is that it permits theautomatic stacking of long, thin, flexible laminae into an interlockedstack, the laminae having cross-sectional shapes with sides that may notsubstantially lie in a common plane.

The invention comprises, in one form thereof, a die assembly forproducing a lamina stack including at least one lamina layer which iscomprised of a plurality of discrete segments. Strip stock is guidedthrough the die assembly and a plurality of laminae and discrete laminasegments are progressively stamped from the strip stock. The laminae andeach of the discrete lamina segments have interlock tabs and/or slotspunched therein and remain attached to the strip stock prior toadvancement to the blanking station at which the choke barrel islocated. At the blanking station, the lamina segments have theirinterlock tabs engaged with the interlock slots of the uppermost laminain the choke barrel immediately prior to the complete separation of thelamina segments from the strip stock material thereby maintaining thelamina segments in proper alignment with each other and the laminaewhich form the remainder of the lamina stack. The choke barrel may alsobe rotatable whereby the laminae may be rotated to correct for thicknessinconsistencies in the strip stock material.

The invention comprises, in another form thereof, a die assembly forproducing a lamina stack including at least one lamina which iscomprised of a plurality of lamina segments and wherein the laminaeforming the stack have more than one predetermined outer perimeterconfiguration. The die assembly provides for the alignment, interlockingand stacking of the lamina segments as described above and also providesa common choke surface on the outer perimeter of each of the laminasegments so that, when the lamina stack is completed, the resultantstack comprising lamina layers having a plurality of outer perimetersand may have a plurality of common choke surfaces on its outer perimeterwhich may extend continuously along the exterior edge of each laminalayer in the stack in a direction parallel to the axis of the laminastack. The laminae are stacked within the choke barrel such that thecommon choke surfaces are in registry with an alignment surface of thechoke barrel.

The invention comprises, in another form thereof, a selectively actuateddie assembly for producing a lamina stack formed from laminae which havemore than one predetermined outer perimeter configuration. Each of thediffering outer perimeter configurations has at least one common chokesurface so that, when the laminae are stacked, the resultant stack mayhave at least one choke surface on its outer perimeter which extendscontinuously along the exterior edge of each lamina in the stack in adirection parallel to the axis of the lamina stack. The laminae are thenstacked in a choke barrel with their common choke surfaces being alignedto create a lamina stack comprised of laminae having a plurality ofouter perimeters and at least one choke surface extending continuouslyin an axial direction across a portion of the outer perimeter of each ofthe laminae. The choke barrel, which may be rotatable, includes analignment surface, the common choke surfaces of the laminae beingstacked in registry with the alignment surface.

The invention comprises, in another form thereof, a method ofmanufacturing a lamina stack, having at least one lamina layer formedfrom a plurality of discrete segments, in a die assembly having a punchand a choke barrel. Strip stock is guided through the die assembly and aplurality of laminae are stamped from the strip stock including at leastone lamina which is comprised of at least two discrete segments. Thelamina segments are maintained in relative alignment by attachment tothe strip stock material as they are advanced through the die assembly.During progression of the discrete segments through the die assemblyinterlock tabs and slots are stamped into each of the lamina segments.When the lamina segments reach the choke barrel, the interlock tabs ofeach of the lamina segments are engaged with the uppermost lamina in thechoke barrel prior to separating the discrete segments from the stripstock to thereby continuously maintain the proper alignment of thelamina segments relative to each other and the other laminae which formthe remainder of the lamina stack.

The invention comprises, in another form thereof, a method ofmanufacturing a lamina stack in a die assembly having a selectivelyactuated punch and a choke barrel. Strip stock is guided through the dieassembly and a plurality of laminae are stamped from the strip stock bythe selectively actuated punch to form laminae having a plurality ofouter perimeter configurations. The laminae each have a common chokesurface which are aligned as the laminae are formed into a stack in thechoke barrel. It is also possible to autorotate the laminae prior tostacking the laminae.

The invention comprises, in another form thereof, a method ofmanufacturing an elongate laminated stack in a die assembly having meansfor guiding strip stock material through the die assembly, stampingmeans and a choke passageway or opening. A first elongate lamina isstamped in the stock material and at least one first interlock means forengaging another lamina is stamped in the first lamina. The first laminais separated from the stock material and placed into the chokepassageway. A second lamina is stamped in the stock material and atleast one second interlock means for engaging another lamina is stampedin the second lamina. The first and second interlocking means are atleast partially engaged, after which the second lamina is separated fromthe stock material and placed into the choke passageway. While in thechoke passageway, only one of the first and second laminae frictionallyengages the choke passageway along its first and second elongate edges.

The invention comprises, in another form thereof, a method ofmanufacturing an elongate stack of laminae in a die assembly havingmeans for guiding strip stock material through the die assembly,stamping means and a choke passageway. A first lamina is stamped in thestock material and at least one first interlock means for engaginganother lamina is stamped in the first lamina. The first lamina isseparated from the sheet stock material to yield a first lamina having afirst outside perimeter shape having an elongate edge and which isplaced into the choke passageway. A second lamina is stamped in thestock material and at least one second interlock means for engaginganother lamina is stamped in the second lamina. The first and secondinterlocking means are at least partially engaged before the secondlamina is separated from the stock material. The second lamina isseparated from the sheet stock material to yield a second laminarsegment having a second outside perimeter shape having an elongate edgeand different than the first outside perimeter shape, and is placed intothe choke passageway. The elongate edge of only one of the first andsecond laminae frictionally engages the choke passageway.

The invention comprises, in another form thereof, a method ofmanufacturing an elongate stack of interlocked laminae in a die assemblyhaving means for guiding strip stock material therethrough, stampingmeans and a choke passageway or opening. The method includes stamping afirst elongated lamina having generally opposed first, second, third,and fourth edges in the strip stock material. At least one firstinterlock element is also stamped into the first lamina, after which thefirst lamina is separated from the strip stock material and placed intothe choke passageway, the first and second edges of the first laminafrictionally engaging the choke passageway. A second elongate laminahaving first, second, third, and fourth edges is stamped in the stripstock material. At least one second interlock element is also stamped inthe second lamina and at least partially engaged with the firstinterlocking element, after which the second lamina is separated fromthe strip stock material and placed into the choke passageway, the firstand second edges of the second lamina frictionally engaging the chokepassageway. The choke passageway frictionally engages along the thirdand fourth edges of only one of the first and second laminae.

The invention comprises, in another form thereof, a die assembly formanufacturing a stack of elongate, slender laminae from strip stockmaterial, which comprises a plurality of punching stations, eachpunching station having a punch for stamping features in strip stockmaterial. The features define elongate laminae each having generallyopposite first and second edges and interlock means for engaging anotherlamina. Each of the laminae are connected to a carrier portion of thestrip stock material. The die assembly further includes aligning meansfor positioning the strip stock material in the die assembly, and ablanking station having a blanking punch disposed over an elongate chokecavity for separating a lamina from the carrier portion of the stripstock.

The invention comprises, in yet another form thereof, an elongate stackof laminae including at least one first lamina and at least one secondlamina, the first lamina being the widest of all laminae in the stack.The second lamina has a width which is less than that of the firstlamina. Each lamina in the stack is interlocked to another lamina.

The invention comprises, in still another form thereof, an elongatestack of interlocked laminae including a first elongate, slender,relatively flexible lamina having a first interlock element and firstand second generally opposed edges defining the ends of the first laminain a first direction of the stack. The first lamina also has third andfourth generally opposed edges defining the ends of the first lamina ina second stack direction. The stack also includes a second elongate,slender, relatively flexible lamina having a second interlock element,which is interlocked with the first interlock element, and first andsecond generally opposed edges defining the ends of the second lamina inthe first stack direction. The first edges of the first and secondlaminae are aligned to define a substantially planar stack surface. Thesecond lamina also has third and fourth generally opposed edges definingthe ends thereof in the second stack direction. One of the third andfourth edges of the first lamina are not aligned with the third andfourth edges of the second lamina.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features and objects of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a plan view of a first strip layout for producing a statorcore having laminae with a plurality of distinguishable outer perimeterconfigurations;

FIG. 2 is a plan view of the stator core created by stacking the laminaeproduced by the strip layout of FIG. 1;

FIG. 3 is a perspective view of the stator core of FIG. 2;

FIG. 4 is a plan view of a second strip layout for producing a statorcore having a plurality of distinguishable outer perimeterconfigurations;

FIG. 4A is an enlarged partial plan view of detail 4A of FIG. 4;

FIG. 4B is an enlarged partial plan view of detail 4B of FIG. 4;

FIG. 5 is a plan view of the stator core produced by stacking thelaminae produced by the strip layout of FIG. 4;

FIG. 6 is a partial perspective view of the stator core of FIG. 5;

FIG. 7 is another partial perspective view of the stator core of FIG. 5;

FIG. 8 is an elevational view of the camming arrangement of aselectively actuated die for manufacturing laminae with a plurality ofouter perimeter configurations;

FIG. 9 is a partial plan view of a die with a rotatable choke barrelhaving alignment surfaces;

FIG. 10 is a cross-sectional view taken along line 10—10 of FIG. 9;

FIG. 11 is a schematic illustration of the interconnections between adie controller, a measuring device, and a die with a rotatable chokebarrel;

FIG. 12 is perspective view of a lamina stack which includes laminalayers comprised of a plurality of discrete segments;

FIG. 13A is a plan view of a lamina forming a portion of the laminastack of FIG. 12;

FIG. 13B is a plan view of a lamina forming a portion of the laminastack of FIG. 12 and which is comprised of a plurality of discretelamina segments;

FIG. 13C is a plan view of a lamina forming a portion of the laminastack of FIG. 12 and which is comprised of a plurality of discretelamina segments;

FIG. 13D is a plan view of a lamina forming a portion of the laminastack of FIG. 12 and which is comprised of a plurality of discretelamina segments;

FIG. 13E is a plan view of a lamina forming a portion of the laminastack of FIG. 12;

FIG. 14 is a schematic cross sectional view of a die assembly at ablanking station at the beginning of a stamping stroke;

FIG. 15 is a schematic cross sectional view of the die assembly of FIG.14 after the guide pin has entered the guide bore;

FIG. 16 is a schematic cross sectional view of the die assembly of FIG.14 wherein the interlock tabs of the discrete lamina segments are beingengaged with the uppermost lamina disposed in the choke barrel;

FIG. 17 is a schematic cross sectional view of the blanking punch ofFIG. 14 separating the discrete lamina segments from the strip stockmaterial;

FIG. 18 is a schematic view of the sheared edge of a thick material;

FIG. 19 is a schematic view of the sheared edges of a plurality oflaminae forming a laminated stack;

FIG. 20 is a perspective view of a long, slender lamina stack producedin accordance with an embodiment of the present invention;

FIG. 21 is a cross sectional end view of the stack shown in FIG. 20,along line 21—21 thereof;

FIG. 22 is a plan view of an embodiment of a strip layout for producingthe stack shown in FIG. 20;

FIG. 23 is a fragmentary plan view of the blanking station of FIG. 22,showing the stack of FIG. 20 in the choke passageway thereof;

FIG. 24 is a fragmentary sectional end view of the die assembly stationshown in FIG. 23, along line 24—24 thereof, a completed initial stackshown in the choke passageway;

FIG. 25 is a fragmentary sectional end view of the die assembly stationshown in FIG. 23, along line 25—25 thereof, a plurality of completedstacks shown in the choke passageway;

FIG. 26 is a schematic cross sectional view of the die assembly at theblanking station of FIG. 22 at the beginning of a stamping stroke, acompleted and a partially completed stack shown in the choke passageway;

FIG. 27 is a schematic cross sectional view of the die assembly of FIG.26 after the guide pin has entered the guide bore, a completed and apartially completed stack shown in the choke passageway;

FIG. 28 is a schematic cross sectional view of the die assembly of FIG.26 wherein the interlock tabs of the lamina being blanked are engagedwith the uppermost lamina disposed in the choke passageway, a completedand a partially completed stack shown in the choke passageway; and

FIG. 29 is a schematic cross sectional view of the blanking punch ofFIG. 26 separating the lamina from the strip stock material, a completedand a partially completed stack shown in the choke passageway.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the drawings representembodiments of the present invention, the drawings are not necessarilyto scale and certain features may be exaggerated in order to betterillustrate and explain the present invention. The exemplifications setout herein illustrate embodiments of the invention, in several forms,and such exemplifications are not to be construed as limiting the scopeof the invention in any manner.

DESCRIPTION OF THE PRESENT INVENTION

The embodiments disclosed below are not intended to be exhaustive orlimit the invention to the precise forms disclosed in the followingdetailed description.

A strip layout showing a stamping progression in accordance with thepresent invention is shown in FIG. 1. The laminae produced by the striplayout of FIG. 1 are used to produce a stator core having projectingflanges on only some of the laminae within each stator core as shown inFIGS. 2 and 3.

At Station No. 1, slots 22 which define the outer perimeter ofprojecting flanges for two adjacent laminae are punched. Pilot pin holes24 used to guide and align strip stock 34 through subsequent stationsare also punched at Station No. 1. Flange defining slots 22 are punchedfor each lamina, even for those laminae which will have the flangesselectively removed at a later station.

Station No. 2 includes a punch which punches stator bore hole 26 in eachlamina. In most cases, this station would comprise either a rotor blankout punch or stator bore hole shave punch. Flanges 31, 32 and 33 definedby slots 22 are selectively removed from some of the laminae at StationNo. 2 as shown by outline 27 of the selectively actuated flange removalpunches.

At Station No. 3, flange bolt holes 28 and flange slots 30 are punched.The strip stock is shown with flanges 31, 32 and 33 at Station Nos. 3-7,however, for laminae which do not have flanges 31, 32 and 33 due to theactuation of the flange removal punches at Station No. 2, the materialcomprising the flanges would not be present. Thus, the punches atStation No. 3 do not have to be selectively actuated. By limiting theuse of selectively actuated dies to only those situations where they areindispensable the cost of the die assembly is minimized.

Stator winding slots 36 for all of the laminae are punched at StationNo. 4. The use of a single punch cluster at Station No. 4 to stampwinding slots 36 for each of the laminae produces a winding slot infinished stator core 42 which has fewer discontinuities and sharp edgesthan a stator core comprised of laminae produced by a plurality of dies.

Station No. 5 is a selectively actuated punch station which is actuatedfor the bottom lamina of each stator stack. Material 38 removed atStation No. 5 would otherwise be formed into interlock tab 40 at StationNo. 6. The punches at Station No. 6 do not have to be selectivelyactuated because if the punches are always operative they would simplynot create any additional interlock features in the bottom laminaeformed at Station No. 5.

At Station 7, all of the laminae are blanked from remaining strip stock34 by severing material bridges 41 and are pressed into a choke barrel.It is not necessary for the punch to engage the entire surface area offlanges 31, 32 and 33. For in the present embodiment the choke barrel isnonrotatable, however, as will be described below, the choke barrelutilized in this embodiment of the present invention may also berotatable. Material bridges 41 are cut at the same location on both theflanged and unflanged laminae, thereby creating common choke surfaces44, as shown in FIGS. 1 and 3, on the edge of each lamina.

The choke barrel (shown schematically in FIG. 11) into which the laminaeare pressed has alignment surfaces which correspond with and engage eachof common choke surfaces 44. The alignment surfaces define an outerperimeter which is equal to or slightly less, e.g., by 0.001 inch, thanthe outer perimeter defined by common choke surfaces 44 to therebyprovide an interference fit engagement with the laminae. Thisinterference fit engagement of each of the laminae maintains the laminaein an aligned position and also resists the movement of the laminaethrough the choke barrel. This fit provides backpressure which allowssubsequent laminae to be pressed into interlocked engagement with thelaminae already in the choke barrel.

When the stack has been completed, the individual common choke surfaces44 of each lamina form stack choke surface 45, shown in FIG. 3, whichextends continuously in an axial direction of the stack across a portionof the outer perimeter of each of the laminae which comprise the stack.

Flanged stator core 42 produced by the laminae punched from strip stock34 of FIG. 1 is shown in FIGS. 2 and 3. A controller is used toselectively actuate the punches at Stations 2 and 5. By actuating thepunches of Station Nos. 2 and 5 in a controlled sequence, laminae may beproduced in the order necessary to form flanged stator core 42.

A second strip layout showing a stamping progression in accordance withthe present invention is shown in FIG. 4. The laminae produced by thestrip layout of FIG. 4 are used to produce a stator core havingprojecting flanges on only some of the laminae within each stator coreas shown in FIGS. 5-7. Prior to reaching Station A, pilot pin holes 46,stator bore hole 48, first ribbed slot 50 and second ribbed slot 52 arepunched during the production of a rotor lamina which is removed fromstrip stock 54 prior to Station A.

At Station A, two common choke surfaces comprising a circular portionwith a minor diameter 63 are defined by stamping edge slots 56. Edgeslots 56 are not perfectly symmetrical about centerline 61 but areslightly offset and extend further to the left as seen in FIG. 4.

Station B is a selectively actuated, or cammed, station at which minorcircular perimeter 64 having minor outer diameter 63 is defined bytriangular punches 58 for certain laminae. Just inside the edges ofcommon choke surfaces 70 defined at Station A, first and second roundedcorners 60 and 62 project inwardly on the punches and thereby cut commonchoke surfaces 70 at a roughly 90° angle and avoid the difficultieswhich can arise when attempting to feather a cut into a preexistingedge.

First and second ribbed slots 50 and 52 also have similar roundedcorners to allow for a cleaner cut. Second ribbed slot 52 is closer tocenterline 51 than first ribbed slot 50; and rounded corners 62 arecloser to centerline 61 than rounded corners 60 as further explainedherein below.

Station C is idle and minor circular perimeter 64 is shown in dashedoutline. The material outside minor perimeter 64 would not be presentfor those laminae which were stamped by the selectively actuated die atStation B.

Winding slots 66 are stamped at Station D for all of the laminae. AtStation E major outside perimeter 67, having major diameter 69, ispunched by means of two punches 68 which form an hourglass shape.Station E does not have to be selectively actuated and removes nomaterial for those laminae which have already had a minor perimeterdefined at Station B. Hourglass shaped punches 68 do not intersectcommon choke surface 70 on the edge of each lamina but instead leaveshort and long locator ribs 72 and 74, respectively.

Station F is selectively actuated and punches tab receiving slot 76 inthose laminae which will form the bottom lamina of each lamina stack 82.A partial cross-sectional view of Station F is shown in FIG. 8 andillustrates the operation of selectively actuated punch 85. Piston 84 isused to control the position of first camming bar 86 which reciprocatesin the horizontal direction to thereby move camming bar 88 in a verticaldirection due to the interaction of camming surfaces 87. When cammingbars 86 and 88 are in the positions shown in solid lines, die punches 90are positioned as shown in FIG. 8. When in this position, die punches 90do not remove material from the strip stock. Die punches 90 are allowedto reciprocate vertically with respect to punch block 93 as well as movevertically as a unit with upper die assembly 89.

When piston 84 moves first camming bar 86 into the position shown indotted outline in FIG. 8, second camming bar 88 is moved into theposition shown by the dotted outline in FIG. 8 due to the interaction ofcamming surfaces 87. In this actuated position second camming bar 88 ismoved downward a short vertical distance 91 and thereby forces punches90 to reciprocate downward distance 92 with respect to punch block 93and into an actuated position. Upper die assembly 89 is shown in itslowermost position with respect to die bed 95 in FIG. 8. As seen in FIG.8, punch tips 90A do not punch strip stock 54 during operation of thedie when punches 90 are not in an actuated position. When actuated,punch tips 90A reach a lowermost position at lines 97 within acooperating aperture (not shown) in die bed 95 when upper die assembly89 is moved downward as a unit. Thus, punches 90 create tab receivingslots 76 in strip stock 54 during operation of the die with the punchesactuated but do not create tab receiving slots 76 during operation ofthe die when the punches are not actuated. Other cammed or selectivelyactuated stations operate in a similar manner. A center interlock may bealternatively used such as described in U.S. patent application Ser. No.07/966,876 filed Oct. 26, 1992, assigned to the assignee of the presentinvention, the disclosure of which is expressly incorporated herein byreference.

At Station G, shown in FIG. 4, interlock tabs 78 are punched. Station His idle, and at Station I the laminae are punched into rotatable chokebarrel 94 (not shown in FIG. 4). Small carrier strip 80 is cut from oneend of the lamina defining common choke surface 71 (shown in FIGS. 4 and6) and, on the opposing side of the lamina, another common choke surface71 is defined along dashed line 81 where the lamina is cut from thestrip stock. Carrier strip 80 interconnects the laminae and allows thelaminae to be transported as a strip between stations before they areblanked into the choke barrel. Other well known means may also be used;such as pushback designs, which are generally impractical for statorcores because of the increased strip width which is required; andsemi-scrapless designs, in which only a single cut, severing the laminafrom the strip stock, is made at the last station.

Rotatable choke barrel 94 is shown in FIGS. 9 and 10. Common chokesurfaces 71, shown in FIG. 6, are defined by cutting edges 96. Carbideinserts 98 having aligning surfaces which engage common choke surfaces70 of each of the laminae project into the interior of choke barrel 94.Similar carbide inserts are located below cutting edges 96 and engagecommon choke surfaces 71 of each of the laminae. Carbide inserts 100engage the outer perimeter surface of only those laminae having a majoroutside diameter.

A servo drive system, mechanical indexer or other means rotates chokebarrel 94 by means of belt 101. The belt, not shown in FIG. 10, islocated in recess 102. Rotating choke barrel 94 engages die bed 95 atsurface 104. Punch 106, shown in FIG. 10, presses the individual laminaeinto interlocked engagement with the laminae which are already withinthe choke barrel for those laminae which have interlock tabs. Therotation of choke rings is known in the art, as shown for example, byU.S. Pat. No. 5,377,115 assigned to the assignee of the presentinvention, the disclosure of which is expressly incorporated herein byreference.

Choke barrel 94 may be rotated between each operation of the dieassembly, for example, by 180° for producing lamina stack 82. Accuraterotation of the laminae is important to maintain vertical registry ofwinding slots 66. The rotation serves several purposes: First, itcorrects for thickness inconsistencies in the strip stock. Second, itprevents ribbed slots 50 and 52 and indentations 60 and 62 from beingaligned. The non-aligned slots and indentations are shown in FIGS. 6 and7. This allows a cup-shaped endshield to be force-fit over the endlaminae having a minor outside perimeter 64 and to abut shoulder 65formed by the laminae having major outside perimeter 67. The endshieldthereby hermetically seals the interior of the stator core. The hermeticseal would not be possible if the laminae were not rotated to preventalignment of ribbed slots 50 and 52 and rounded corners 60 and 62 on thelaminae having minor outside perimeter 64. Providing a hermeticallysealed endshield allows a motor which incorporates stator core 82 to besafely used in environments where flammable vapors are present.Although, the disclosed embodiment rotates each lamina 180° with respectto the previous lamina, other angles and counts (or frequencies) ofautorotation may also be used.

The individual common choke surfaces 70 and 71 disposed on the outerperimeter of each lamina form choke surfaces 73 and 75, respectively,which extend continuously in an axial direction of the stack across aportion of the outer perimeter of each of the laminae which comprisestator stack 82 as illustrated in FIGS. 6 and 7. Common choke surfaces70 and 71 are pressed into engaging contact with aligning surfaces 99 ofcarbide inserts 98 when the laminae are blanked into rotatable chokebarrel 94.

FIG. 11 provides a schematic illustration of the die assemblies used tomanufacture lamina stacks 42 and 82. In FIG. 11, initial station 112corresponds to Station No. 1 and Station A for the embodiments describedabove, and to Station No. I for the embodiment discussed below withregard to FIG. 22, while final or blanking station 114 corresponds toStation No. 7, Station I (above-described embodiments) and Station No.VI (below-described embodiment). FIG. 11 also includes schematicrepresentations of selectively actuated punch stations 85 whichcorrespond to Stations 2 and 5, and B and F, discussed above, FIG. 11does not, however, include representations of each of the remainingstations. Choke barrel 94 can be either stationary or rotatable and doesnot require a communications link with controller 108 in all embodimentsof the invention.

Controller 108 is used to control selectively actuated punches 85 andmay be used to control the autorotation of choke barrel 94 or passageway272, which is discussed further below. Choke barrel 94 or passageway 272may also be stationary or employ a mechanical indexer, in which casecontroller 108 would not need to be linked thereto. The controller canbe programmed to produce laminae in the alignment necessary to producethe desired stator cores. It is also possible, but not required, toemploy measuring device 110, shown schematically in FIG. 11, todetermine the thickness of the sheet stock at one or more points alongits width. The measured thickness values would be transmitted tocontroller 108. Controller 108 would then be used to calculate thenumber of laminae which are required to achieve the desired height ofthe lamina stack, preferably by calculating the number of laminaerequired for each stack segment having a particular outside perimeterconfiguration.

Instead of measuring the strip stock at two different locations alongits width and using a measured strip stock thickness inconsistency tocalculate the amount of rotation required, the irregularities present inthe strip stock can be evenly distributed about the lamina stack axis byrotating all of the laminae a predetermined amount without explicitlycalculating the thickness inconsistency.

Autorotation of laminae to correct for thickness variations is known inthe art and one such method is disclosed in U.S. Pat. No. 5,359,763assigned to the assignee of the present invention, the disclosure ofwhich is expressly incorporated herein by reference. Control of thestack height can also involve the use of a coreweighing system asdisclosed in U.S. Pat. No. 5,365,021 assigned to the assignee of thepresent invention, the disclosure of which is expressly incorporatedherein by reference.

In a cordance with another embodiment of the present invention, FIG. 12illustrates lamina stack 116 having laminae with a plurality of outerperimeter configurations and which includes several laminae or laminalayers which are comprised of a plurality of discrete lamina segments.The individual lamina layers which are used to form lamina stack 116 areillustrated in FIGS. 13A-13E.

Lamina 118 is shown in FIG. 13A and has a continuous and unbroken outerperimeter. Lamina 118 has its interlock tabs 144 completely removedthereby leaving only interlock slots 146 and forming bottom lamina 118of stack 116 which will not interlock with a lamina stack positionedimmediately below bottom lamina 118 in choke barrel 148. Lamina 120,shown in FIG. 13B, is comprised of discrete lamina segments 121 and 122,and has an outer perimeter configuration which defines openings 123B and124B. Lamina 126, shown in FIG. 13C, is comprised of discrete laminasegments 127 and 128, and has an outer perimeter which defines openings123C and 124C. Lamina 134, shown in FIG. 13D, is comprised of discretelamina components 135 and 136, and has an outer perimeter configurationwhich defines openings 123D and 124D. Lamina 134 also includesprojecting flanges 132. Lamina 140 is shown in FIG. 13E and hasinterlock tabs 144 but is otherwise similar to lamina 118. The “recipe”for lamina stack 116 from bottom lamina through final lamina is lamina118, lamina 140, lamina 126, lamina 126, lamina 134, lamina 120, lamina120, lamina 140, and lamina 140.

The various features, including interlock tabs, of laminae 118, 120,126, 134, 140 are formed by progressively stamping a length of stripstock material by actuating punches in a controlled sequence in a mannersimilar to that described above for forming the laminae of stacks 42 and82. After laminae 118, 120, 126, 134 and 140 have been stacked to formlamina stack 116, individual lamina openings 123B, 123C and 123D arealigned and form opening 123. Likewise, individual lamina openings 124B,124C and 124D form opening 124 in the opposite side of lamina stack 116.

The bottom lamina 118 is followed by a lamina 140 which has interlocktabs 144 formed therein which engage bottom lamina 118 and leavecorresponding interlock slots 146 for engagement by the interlock tabsof the upper adjacent lamina. The remaining discrete lamina components121, 122, 127, 128, 135 and 136 each have interlock tabs 144 and slots146 formed therein.

Lamina stack 116 includes laminae which define a plurality of outerperimeter configurations and which utilize common choke surfaces 150.Common choke surfaces 150 are located on the corners of each of thelaminae and lamina segments. The locations of common choke surfaces 150are shown in FIG. 13E. Common choke surfaces 150 are also shown in theperspective view of FIG. 12. The interior of choke barrel 148 includesalignment surfaces which engage common choke surfaces 150 of each of thelaminae and lamina segments which comprise lamina stack 116 to maintainthe laminae in an aligned position and resist the downward movement ofthe lamina stack through the choke barrel. Resistance to downwardmovement in the choke barrel provides the back pressure necessary toengage the interlock tabs of the laminae when a lamina is pressed intoengagement with a partially formed stack in choke barrel 148.

Choke barrel 148 is a steel choke barrel with the alignment surfacesformed integrally with the remaining interior surface of choke barrel148. Alternatively, carbide inserts could be used to form the alignmentsurfaces. The remaining interior surface of choke barrel 148 isconfigured to allow all of the lamina configurations used to form stack116 to enter choke barrel 148. The remaining portion of the choke barrelinterior surface is configured so that the only engagement of chokebarrel 148 with the individual lamina layers occurs at the alignmentsurfaces, in other words, the interior of the choke barrel, except forat the alignment surfaces, does not conform to the outer perimeter ofany of the laminae. Alternatively, the remaining portion of the chokebarrel interior surface could engage portions of the laminae alongportions of the “larger” outer perimeters at locations other than thealignment surfaces.

The alignment surfaces of choke barrel 148 provide an interference fitwith the laminae used to form stack 116. Excessively tight interferencefits are undesirable because they can lead to a bowing of the individuallaminae which are pressed into the choke barrel. The use of discretelamina segments to form an individual lamina layer, such as laminae 120,126 and 134 in stack 116, may increase the susceptibility of a laminalayer to undesirable bowing and distortion. The geometric configurationof the individual laminae and lamina segments and the physicalproperties of strip stock material 154 are both factors in determiningthe susceptibility of a lamina layer to undesirable bowing ordistortion.

To minimize the risk of undesirable bowing, the alignment surfaces ofchoke barrel 148 utilize a relatively light interference fit whichexerts a reduced pressure on each individual lamina but which developsback pressure over a relatively greater vertical depth 152 to therebyprovide an adequate total back pressure for engagement of interlock tabs144. For example, in an application wherein a conventional interferencefit might involve a 0.001 inch interference fit and a choke depth of1.25 inches, the present application might utilize a 0.0002 to 0.0005inch interference fit and a choke depth of 3 inches. Resistance todownward movement within the choke barrel is needed to facilitate theengagement of interlock tabs 144 of the lamina being blanked withinterlock slots 146 of the uppermost lamina in the choke barrel. Thepressure exerted on the individual laminae not only provides resistanceto downward motion through the choke barrel but also helps maintain thelaminae in proper alignment.

Due to the relatively short height of lamina stack 116, i.e., ninelaminae, the compounding of the thickness inconsistencies of theindividual laminae is not likely to create significant variances in thefinal dimensions of lamina stack 116. Thus, illustrated choke barrel 148is non-rotatable. However, alternative embodiments could utilize arotatable choke barrel.

The stacking of a plurality discrete lamina segments to form a singlelamina layer is schematically illustrated in FIGS. 14-17. FIGS. 14-17sequentially illustrate the blanking station, at which discrete laminasegments 127, 128 are automatically stacked within choke barrel 148,during a single die stroke.

The laminae and lamina segments which comprise lamina stack 116 areformed by stamping various features in strip stock material 154 as itprogresses through the die assembly prior to reaching the blankingstation illustrated in FIGS. 14-17. The laminae and lamina segments areattached to the strip stock material through strip stock materialbridges which are severed by blanking punch 156. Strip stock materialincludes pilot pin holes 158 which form apertures in the carrier portionof the strip stock material, i.e., that portion of strip stock materialwhich is not used to form laminae. Pilot pin holes 158 are used tomaintain the strip stock material in a desired position relative to thedie stations as it is stamped during its advancement through the dieassembly. As can be seen in FIGS. 14-17, pilot pin 160 passes throughpilot pin hole 158 and enters guide bore 162 to properly locate stripstock material 154 and the laminae and lamina segments which areattached thereto by the sheet stock material bridges relative to theblanking station prior to stamping strip stock material 154. Althoughonly one pilot pin 160 is illustrated, pilot pins are located adjacenteach punching station of the die assembly to maintain strip stockmaterial 154 in proper alignment during stamping operations.

FIG. 14 schematically illustrates a portion of upper die assembly 164and lower die bed 166. Upper die assembly 164 reciprocates vertically,together with pilot pin 160 and blanking punch 156, to stamp thelaminae. Blanking punch 156 severs the material bridges connecting thelaminae to the remainder of strip stock material 154. Blanking punch 156also pushes the laminae into engagement with the uppermost lamina layerdisposed in choke barrel 148.

Blanking punch 156 includes staking punch inserts 168 which extend belowthe bottom surface of the blanking punch by a distance designated 170 inFIG. 14. Staking punches 168 correspond to the location of interlocktabs 144 and enter lamina slot 146 of the lamina or lamina segmentsbeing blanked from strip stock 154 and positively engage the respectivelamina tabs 144 b of the lamina being blanked with the respectiveinterlock slots 146 u of the uppermost lamina layer disposed in chokebarrel 148.

Staking punches 168 are held in a fixed position relative to blankingpunch 156 and each includes head 169 which is seated in a counterbore inblanking punch 156. A grind collar (not shown) may be located below head169 to permit the lowering of staking punch 168 relative to blankingpunch 156. Lowering of the staking punch might be necessary due tochipping or wear of staking punch 168 or to accommodate differentinterlock tab depths.

A number of different interlock tab designs are known in the art and thetab design will influence the selection of the appropriate tab depth. Inone design, three of four sides of a tab are severed from the remainderof the lamina and the tab may be distended below the bottom surface ofthe lamina by a relatively large distance. In the illustratedembodiment, lamina stack 116 utilizes an alternative design in which noportion of interlock tab 144 is completely severed from the surroundinglamina material. Instead, interlock tab 144 is partially blanked fromthe surrounding material, deforming, but not severing, the material atthe edges of interlock tab 144. Tabs 144 extend below the bottom of theremainder of the lamina by approximately ½ to ⅓ the thickness of thelamina layer. Alternative embodiments of the present invention mayemploy alternative interlock styles or have the interlock tabs extend agreater or less distance below the remainder of the lamina.

The thickness of the lamina is designated 173 in FIG. 14. The distanceby which tab 144 extends below the lower lamina surface is designated172 in FIG. 14 and is equivalent to distance 170 staking punch 168extends below blanking punch 156 and is approximately one half ofthickness 173. The length designations shown in FIG. 14 are includedmerely to provide a convenient mechanism for graphically identifying thelengths and spatial relationships discussed herein and are notnecessarily to scale.

As discussed above, staking punches 168 are used to ensure engagement ofinterlock tabs 144 into interlock slots 146 and to prevent interlocktabs 144 from being forced upwardly into the horizontal plane of theremainder of the lamina when tab 144 engages the uppermost lamina inchoke barrel 148. Staking punches 168 extend a distance 170 below theblanking punch 156. Distance 170 is equivalent to the depth it isdesired to have interlock tab 144 enter interlock slot 146 of the loweradjacent lamina layer. Generally, this distance 170 will be equivalentto distance 172 which interlock tab 144 extends below the lower surfaceof strip stock material 154 when tab 144 is formed.

Each of the laminae and lamina segments of stack 116 has at least oneinterlock feature formed therein. The bottom lamina of each stack,however, has its interlock tabs completely blanked, i.e., removed, toprevent bottom lamina 118 from being engaged with the uppermost laminaof the previously formed stack when the bottom lamina 118 is separatedfrom the strip stock material and pushed into the choke barrel.Interlocking tabs 144 and slots 146 of adjacent lamina layers maintainsthe lamina layers in proper relative alignment both when the stack iswithin choke barrel 148 and after the stack has been removed from chokebarrel 148.

Stock lifters 174 are used to prevent interlock tabs 144 from beingbiased upwardly into the horizontal plane of strip stock material 154 orfrom being snagged on lower die bed 166 during the progressive movementof strip stock material 154. Stock lifters 174 are biased upwards bysprings 176 and lift strip stock material 154 above the upper surface oflower die bed 166 when strip stock material 154 is being advancedbetween die stamping strokes. Strip stock material 154 is lifted bystock lifters 174 a distance designated 175 in FIG. 14. Lifter distance175 is often times equivalent to approximately 1.5 times thickness 173of strip stock material 154 to provide an ample clearance. Theillustrated stock lifters 174 are cylindrical. However, other types ofstock lifters, such as bar type lifters, are known in the art and canalso be used with the present invention.

FIG. 14 illustrates the relative positions of upper die assembly 164,punches 156, 168, lower die bed 166 and strip stock material 154 at theinitiation of a stamping stroke at the blanking station of the dieassembly. FIG. 15 illustrates the die assembly during the downstrokeafter pilot pin 160 has extended through pilot pin hole 158 and hasentered guide bore 162 to thereby properly locate strip stock material154 and lamina segments 122, 124 which are attached thereto. Shortlyafter pilot pin 160 has properly aligned strip stock material 154, andthe laminae and lamina segments attached thereto by material bridges,staking punches 168 enter interlock slots 146 of the lamina layer whichis about to be blanked. Shortly after staking punches 168 enterinterlock slots 146, blanking punch 156 engages the upper surface of thelamina layer.

Stock lifter spring 176 has been compressed and strip stock material 154is pressed against the upper surface of lower die bed 166 in FIG. 15.Strip stock material 154 may be pressed against lower die bed 166 byengagement with the downwardly moving punches or by another suitablemechanism, such as a spring stripper, attached to upper die assembly 164which presses the strip stock material against lower die bed 166 priorto the engagement of the punches and strip stock material 154.

FIG. 16 illustrates the blanking station after the blanking punch hasbegun to sever lamina segments 122 and 124 from the remainder of stripstock material 154. As shown schematically in FIG. 16, interlock tabs144 b of lamina segments 122, 124 are already partially engaged withinterlock slots 146 u of the uppermost lamina layer in choke barrel 148.The partial engagement of interlock tabs 144 b and interlock slots 146 uoccurs prior to the complete separation of lamina segments 122, 124 fromthe remainder of the strip stock material.

Engaging interlock tabs 144 b of the discrete lamina segments 122, 124prior to completely severing lamina segments 122, 124 from the remainderof the strip stock material 154 permits the aligned stacking of lamina120 even though the segments, once blanked, become separated from eachother. The proper and positive alignment of discrete lamina segments122, 124 is continuously maintained during the stamping process.Initially, guide pin 160 maintains the proper alignment of laminasegments 122, 124 by aligning strip stock material 154. Prior tocompletely severing lamina segments 122, 124 from strip stock material154, interlock tabs 144 b of the discrete lamina segments being blankedare engaged with interlock slots 146 u of the uppermost lamina layer inchoke barrel 148 to maintain the alignment of the discrete laminasegments.

To accomplish the engagement of interlock tabs 144 b and interlock slots146 u of adjacent laminae prior to the complete severing of the blankedlamina layer from strip stock material 154 the uppermost lamina must bepositioned in choke barrel 148 near the upper surface of lower die bed166. The uppermost lamina is positioned distance 178 below the entranceof the choke barrel located in the upper surface of the lower die bed.

Distance 178 (FIG. 14) is determined by the distance blanking punch 156enters choke barrel 148 at the end of the die assembly downstroke, asshown in FIG. 17. Punch entry distance 178 is typically greater than thethickness 173 of the strip stock material in conventional dieassemblies. For example, for a strip stock thickness 173 equivalent to0.025 inch, a conventional die assembly would often have a punch entrybetween 0.030 and 0.035 inch.

The present invention, however, utilizes a much smaller punch entrydistance 178 (which may be as small as zero) which ensures thatinterlock tabs 144 of the blanked lamina layer are engaged with theuppermost lamina layer in the choke barrel prior to completely severingthe lamina layer being blanked. For example, with reference to FIG. 14,by utilizing a distance 178 which is smaller than distance 172, tabs 144b will be partially interlocked with slots 146 u when the die assemblyreaches the position shown in FIG. 15. Alternatively, distance 178 canbe equivalent to distance 170 as shown in FIGS. 14-17 and interlock tabs144 b will be engaged with slots 146 u as the lamina layer being blankedis being severed from strip stock material 154 but prior to completeseparation as shown in FIG. 16. It may also be possible to have adistance 178 slightly larger than distance 170 and still provide for thepartial interlocking of tabs 144 b and slots 146 u prior to completeseparation of the lamina layer. The partial interlocking in such anarrangement, however, would be minimal.

When a plurality of discrete lamina segments are used to form a singlelamina layer, the pressure exerted against each common choke surface 150by the alignment surfaces of choke barrel 148 will not necessarily becounterbalanced by a force created by an opposing alignment surface.Interlock tabs 144, however, are disposed near common choke surfaces 150and provide resistance to the pressure exerted by the alignment surfacesand thereby maintain discrete lamina segments in an aligned position.Placing interlock tabs 144 near common choke surfaces 150 also minimizesany bowing or distortion of the lamina by limiting the area of thelamina which is stressed by the pressure applied by the alignmentsurfaces.

Blanking punch 156 severs the material bridges which connect laminasegments 122, 124 to the remainder of strip stock material 154 incooperation with cutting edges on the upper lip of choke barrel 148.Typically, after blanking punch 156 has sheared the lamina layer to adepth which is approximately ⅓ of the lamina thickness, the lower ⅔ ofthe strip stock material will fracture and the lamina layer will becompletely separated from the strip stock material. The use of a softer,more elastic strip stock material, however, would permit the blankingpunch to enter the strip stock material for more than ⅓ of the laminathickness and produce a lamina with a smaller fracture zone. Asdiscussed above, the proper alignment of discrete lamina segments 122,124 is maintained by engagement of interlock tabs 144 b prior to thefracturing of the strip stock material attaching discrete laminasegments 122, 124 to the remainder of strip stock material 154.

The downstroke is finished by pushing discrete lamina segments 122, 124into further engagement with the uppermost lamina in choke barrel 148and pushing lamina segments 122, 124 to depth 178 below the uppersurface of lower die bed 166 as schematically illustrated in FIG. 17.After blanking punch 156 is retracted, stock lifters 74 elevate stripstock material 154, strip stock material 154 is advanced within the dieassembly, and the stamping cycle is repeated. A die assembly embodyingthe present invention may be operated at speeds which are typical forinterlocked laminae, e.g., 300 or more strokes per minute. The maximumspeed of operation of any particular die assembly is dependent upon anumber of different variables relating to the complexity of the dieassembly and the material handling requirements imposed upon the dieassembly by the dimensions and configuration of the lamina stack beingmanufactured. For most lamina stack and die assembly designs, however,the stamping and stacking of two discrete lamina segments to form asingle layer in a lamina stack should not, by itself, have a directimpact upon the speed at which individual die assemblies are operated.

The ability to automatically stamp and stack a plurality of laminaewhich include a lamina layer formed by a plurality of discrete laminasegments permits the economical manufacture of parts which mightotherwise be more expensively manufactured from a single layer ofmaterial. For example, the ability to stack lamina layers having aplurality of discrete lamina segments permits the manufacture, in asingle operation, of laminated parts wherein a plurality of apertures orother discontinuities are located in the part so as to prevent the useof an integral lamina for one or more layers of the stack. Conventionalmanufacture of such parts often involves the stamping of a single,relatively thick, material layer and forming the apertures or otherdiscontinuities with secondary operations such as drilling or milling.Additionally, as described in greater detail below, a higher qualitystamped edge can be realized by utilizing a plurality of laminae insteadof stamping a single thick material layer.

FIGS. 18 and 19 schematically, and in exaggerated fashion for the sakeof clarity, illustrate edges which have been sheared by a stampingprocess. With reference to thick material 180, the process of stamping apart from a sheet of stock material with blanking punch 156 will bedescribed in greater detail. When punch 156 first engages the material,the material will deform plastically before it is sheared. The initialplastic deformation results in rounded corner 182. The material willthen be sheared by the penetration of the punch until the lower portionof the strip stock material fractures. Typically, the punch willpenetrate approximately ⅓ of the lamina thickness before the lower ⅔ ofthe lamina fractures. This leaves a relatively smooth shear cut band184, marked by cross hatching, and a rougher fracture zone 186. Thinlaminae 190 shown in FIG. 19 have rounded corners 192, shear cut bands194 and fracture zones 196 on their cut edges which are proportionallysimilar to those of thick material 180, e.g., shear band 194 isapproximately ⅓ the thickness of the lamina material. Althoughproportional, the magnitude of the individual edge depressions which arelocated in the fracture zone 196 of thinner laminae 190 are smaller thanthe depressions located in fracture zone 186 of thick material 180.Rounded edge depression 182 shown in FIG. 19 is also smaller thandepression 192 shown in FIG. 18. Thus, by utilizing a plurality ofthinner laminae 190 instead of thick material 180, one can manufacture apart having an edge wherein the magnitude of the roughness is reducedand the clean shear cut band is more evenly distributed. For example, aclutch plate having the form of a splined disk could be formed bystamping and stacking ten 0.025 inch laminae to thereby provide a higherquality edge surface than a single 0.25 inch layer of stamped material.

In accordance with yet another embodiment of the present invention, FIG.20 illustrates long, slender lamina stack 200 having laminae ofdiffering widths which are stacked so as to form a generally cylindricalpart, with each lamina having a common length. Although stack 200 isgenerally cylindrical, it is to be understood that this is but onepossible embodiment of a stack produced according to the presentinvention; other embodiments having other shapes are to be consideredwithin the scope of the present invention. In the shown embodiment ofthe present invention, the individual laminae comprising stack 200 arestamped from the strip stock material such that the length of eachlamina lies along the grain 203 of the material, i.e., along thelongitudinal directions of the strip stock material. Material grain 203is shown in FIGS. 20 and 22. This stamping orientation provides eachlamina and thus stack 200 with electrical conductivity properties whichdiffer from what would result if the laminae were stamped from the stripstock material such that the length of each lamina lies across the grainof the material, i.e., along the strip stock material width, which maybe an important consideration depending on the application for whichstack 200 is used. Further, each lamina in stack 200 may be made ofsteel and may or may not be coated with a dielectric material 201 (FIGS.21 and 22). Those skilled in the art will appreciate that the processand apparatus of the present invention may be readily applied to producestacks having “cross grain” lamina lengths. Such a “cross grain”embodiment of the present invention would provide the advantage ofallowing a shorter die assembly, which requires less space. Moreover,those skilled in the art will recognize that multiple die assemblies asdescribed hereinbelow may be arranged in parallel and “ganged” such thateach die assembly apparatus and process is commonly controlled by asingle controller 108 (FIG. 11). It is also envisioned thatcorresponding punches in each die assembly may utilize a singlepneumatic cylinder for their simultaneous actuation.

A cross sectional view of cylindrical stack 200 through its interlockingtabs and slots is shown in FIG. 21. As shown in FIGS. 20, 21, stack 200comprises an equal number of laminae disposed on opposite sides ofcentral plane 202, with midmost laminae 204, 206, which are identical,being the widest in the stack, their first and second side edges 208,210, respectively, in frictional contact with the adjacent chokesurfaces during the stack assembly operation, as further describedhereinbelow. Each of the laminae in stack 200 is of a common length L(FIG. 20) and each has a first and second end edges 212, 214,respectively which define opposite end surfaces 216, 218. The first andsecond end edges 212, 214 of each lamina in stack 200 are in frictionalcontact with the adjacent choke surfaces during the stack assemblyoperation. With reference to FIGS. 20 and 21, it is shown that eachlamina lies in a plane substantially normal to axis 217. The outerperimeter of widest lamina 204 or 206, defined by its edges side and endedges 208, 210, 212 and 214, when projected in a direction parallel toaxis 217, forms a boundary within which the similarly defined outerperimeter of any other lamina in stack 200 is entirely located. It canbe readily visualized that the portions of the outer perimeter of eachnarrower lamina defined by that lamina's first and second side edges 208and 210 are spaced from that boundary. Further, the first and second endedges 212, 214 of each lamina in stack 200 are provided with notch 219which, when the individual laminae are stacked, form a straight grooveor slot along end surfaces 216, 218 of stack 200. As illustrated, notch219 has a triangular shape, but may be of another shape (e.g.,rectangular or semicircular) suitable to help maintain the correctposition of the laminae or the stack within the choke passageway asdescribed further below.

As seen in FIG. 21, bottommost lamina 220 and topmost lamina 222 ofstack 200 are of a common width, with topmost lamina 222 provided withan interlock tab 224 which engages slot 226 of adjacent lamina 228 whichit overlies, and bottommost lamina 220 provided only with a slot 230which receives tab 232 of overlying lamina 234, which is identical tolamina 228. Although stack 200 is cylindrical, those skilled in the artwill appreciate that the method and apparatus for its manufacture hereindescribed may be adapted to produce long, slender lamina stacks havingother shapes and having cross sectional sides which do not liesubstantially in planes parallel with the direction of travel of thestack through the choke opening or passageway. Further, althoughcylindrical stack 200 comprises two widest laminae (204, 206) havingside edges which frictionally engage the adjacent choke surfaces, it isenvisioned that a long, slender stack produced according to the presentinvention may comprise only a single lamina of greatest width, the sideedges of which engage the adjacent choke surfaces, and that the widestlamina(s) need not be vertically middlemost in the stack, as laminae204, 206 are. Indeed, the widest lamina(s) may be anywhere in the stackand, if a plurality of widest laminae are included, they need not beadjacent to one another.

A strip layout showing a stamping progression in accordance with thepresent invention is shown in FIG. 22. The laminae produced by the striplayout of FIG. 22 are used to produce a cylindrical stack 200, althoughonly some of stations which produce the many laminae of various widthsare represented.

At Station No. I, material is punched (removed) from strip stock 236which defines first and second side edges 208, 210 of bottommost lamina220 and topmost lamina 222, which are of common width (see FIG. 21).Pilot pin hole 238, used to guide and align the strip stock 236 atsubsequent stations, is also punched at Station No. I. Punches 240, 242which form first and second side edges 208, 210 of lamina 220 and 222 atStation No. I are selectively actuated in the above-described manner,while punch 244 which forms pilot pin hole 238 is actuated during eachpunch cycle. Punches 240 and 242 may, of course, comprise portions of asingle, selectively actuated punch, as may each pair of punches at eachof the subsequent stations.

Station No. II includes selectively actuated punches 246, 248 whichremove material from strip stock 236 to define first and second sideedges 208, 210 of lamina 234 and lamina 228, which are of common widthand which are respectively adjacent bottommost lamina 220 and topmostlamina 222 in stack 200 (see FIG. 21).

At Station No. III, selectively actuated punches 250, 252 removematerial from strip stock 236 to define first and second side edges 208,210 of lamina 254 and lamina 256, which are of common width and whichare respectively adjacent laminae 234 and 228 in stack 200 (see FIG.21).

Between Stations Nos. III and IV are located a plurality of otherstations having selectively actuated punches which define first andsecond side edges 208, 210 of the other laminae located above widestlamina 204 and below widest lamina 206 in stack 200.

Station No. IV is a selectively actuated punch station which is actuatedfor only the bottom lamina (220) of each stack. The material removedfrom the strip stock by punches 258, 260 at Station No. IV wouldotherwise be formed into an interlock tab and slot at Station No. V.

At Station No. V, punches 262, 264 remove material from strip stock 236to define first and second side edges 208, 210 of middlemost laminae204, 206, which are of common width. Punches 266, 268 provide theinterlocking tabs and slots in each lamina of stack 200 except forbottommost lamina 220 (see FIG. 21). The punches at Station No. V do nothave to be selectively actuated because if the punches are alwaysoperative they would simply not remove any additional material from thesides of any of the laminae which lie above widest lamina 204 or belowwidest lamina 206, or create any additional interlock features inbottommost lamina 220. By limiting the use of selectively actuated diesto only those situations where they are indispensable the cost of thedie assembly is minimized.

At Station No. VI, all of the laminae are blanked from the remainingstrip stock 236. Blanking punch 270, which is not selectively actuated,severs the laminae therefrom, forms their first and second longitudinalend edges 212, 214, and presses them into choke passageway or opening272. Blanking punch 270 is provided with notch 273 on opposed sidesthere of which cooperate with mating protrusions 271 (FIGS. 22, 23) inopposed sides of the blanking die for forming notch 219 in each laminaas it is blanked from strip stock material 236. Due to the relativelyshort height of lamina stack 200, the compounding of the thicknessinconsistencies of the individual laminae is not likely to createsignificant parallelism concerns in stack 200. Thus, illustrated chokepassageway or opening 272 is non-rotatable. If the stack is to besubstantially tall, however, and the symmetry of the individual laminaeabout their longitudinal axes allows the choke passageway to accommodateit, the choke passageway and the elongate stack(s) therein may berotated 180°.

As in the above-described embodiments, choke passageway 272 (shownschematically in FIG. 11) into which the laminae are pressed hasalignment surfaces which correspond with and frictionally engage firstand second end surfaces 216, 218 and first and second side edges 208,210 of widest laminae 204, 206. The alignment surfaces of chokepassageway define an outer perimeter which is equal to or slightly less,e.g., by 0.001 inch, than the outer perimeter defined by first andsecond edges 208, 210 of widest laminae 204, 206 and first and secondend edges 212, 214 of each lamina to thereby provide an interference fitengagement with the laminae. This interference fit engagement of each ofthe laminae maintains the laminae in an aligned position and alsoresists the movement of the laminae through the choke passageway. Thisallows subsequent laminae to be pressed into interlocked engagement withthe laminae already in the choke passageway. To further ensure properorientation of laminae or completed stacks in choke passageway 272,protrusions 271 in the blanking die, with which punch notches 273cooperate, continually extend into passageway 272 along the opposed endsurfaces thereof, forming ridges 275 (FIGS. 22, 23) thereon. At eachrespective end edge 212, 214 of a lamina, notch 219 is slidably receivedon ridge 275, thus ensuring that those individual laminae which haveinsufficient width to engage choke passageway side surfaces 278, 280remain properly positioned laterally. The sliding engagement of notches219 over ridges 275 is particularly useful in maintaining the alignmentof the laminae below the lowermost widest lamina. For example, inproducing cylindrical stack 200, the engagement of notches 219 on ridges275 ensures that a partial stack consisting only of bottommost lamina220 up to and including lamina 281 (the lamina which is adjacently belowlower middle and widest lamina 206; see FIGS. 24, 25) remains correctlypositioned in choke passageway 272. Otherwise, such a partial stackwould depend solely on the frictional engagement of its laminae's endedges 212, 214 with adjacent choke end surfaces 282, 284, respectively,for maintaining its proper orientation in the choke passageway. Further,the engagement of the grooves in stack end surfaces 216, 218, which areformed by aligned notches 19, over ridges 275 provided on adjacent chokeend surfaces 282, 284, respectively, preclude the possibility of stack200 inadvertently rotating about its longitudinal axis within passageway272. Notches 219 may frictionally engage ridges 275 or, alternatively,the cross sections of ridges 275 may be slightly undersized vis-a-visblanking die protrusions 271, thus providing a slight clearance betweennotches 219 and ridges 275. Those skilled in the art will recognizethat, conversely, a notch may instead be provided in opposite sides ofblanking die 294, extending as grooves in choke end surfaces 282, 284.Protrusions may then be provided in opposite sides of blanking punch 270which would form protrusions in each lamina, the lamina protrusionsslidably received in the grooves formed in choke passageway 272, in themanner described above, for maintaining proper orientation of thelaminae or stacks in the choke passageway.

Notably, it may not be necessary for choke passageway side surfaces 278,280 to continuously contact first and second edges 208, 210 of widestlaminae 204, 206, as shown in FIGS. 22 and 23. Indeed, choke passageway272 may be provided with downwardly-extending grooves or carbide barinserts (not shown) which define intermittent side surfaces 278, 280which contact first and second side edges 208, 210 of widest laminae204, 206 only at longitudinally spaced contact areas. Such spacedcontact of the choke side walls 278, 280 with edges 208, 210 of thewidest laminae may be designed to provide stack 200 with the properresistance to movement along choke passageway 272 and to preventpossible buckling, bending or rotation of the stack or individuallaminae while in the choke passageway. Further, as seen in FIG. 23, thejunctures of side surfaces 278, 280 and end surfaces 282, 284 of chokepassageway 272 may be provided with reliefs 286 which extend into sidesurfaces 278, 280 to ensure that the longitudinal ends of widest laminae204, 206 contact the choke passageway only at their first and second endedges 212, 214, allowing better control of the stack's resistance tomovement through the choke. Thus, when the stack has been completed, theindividual common first and second end edges 212, 214 of each laminaform first and second stack end choke surfaces 216, 218.

Choke passageway 272 ordinarily contains a plurality of stacks 200, and,as will be discussed further hereinbelow, for each stack 200 in thechoke passageway, the frictional engagement of its surfaces 216, 218 andthe portions of first and second side edges 208, 210 of its widestlaminae 204, 206 which are in contact with choke side walls 278, 280contribute a portion of the overall frictional resistance which holdsthe topmost lamina in the choke passageway in place for interlockingwith an overlying lamina of the same stack. Resistance to downwardmovement in the choke barrel provides the back pressure necessary toengage the interlock tabs of the laminae when the overlying lamina ispressed into engagement with the remainder of a partially formed stackin choke passageway 272.

Referring to FIG. 24, during the manufacture of the initial stacks 200,the back pressure otherwise provided by a plurality of completed stackswithin choke passageway 272 may be provided by plug 288, which may bemade of plastic, wood or other suitable material. Plug 288 is ofsufficient circumferential size and thickness that once forced intochoke passageway 272, sufficient resistance to movement of theindividual laminae and stacks 200 is provided for the tabs and slots tointerlock. Plug 288 is placed in the choke passageway such that itsupper surface 290 is initially flush with upper surface 292 of lowerblanking die bed 294. Alternatively, a hydraulic or pneumaticbackpressure device (not shown), such as known in the art, may be usedin lieu of plug 288 to provide resistance to movement of the laminae ofthe initial stacks until a sufficient plurality of stacks has beenaccumulated in passageway 272. Once choke passageway 272 is completelyfilled with a plurality of stacks 200, which provide sufficientfrictional engagement with the engaging surfaces of the choke to createsufficient back pressure for interlocking the tabs and slots of theindividual stacks 200, plug 288 will drop out of the choke passageway,no longer needed until the next time the process begins again with aclear choke passageway. The size of plug 288, the number of stacks 200which are to be contained within passageway 272, the resistance tomovement through passageway 272 each stack 200 provides, and theresistance necessary to interlock the tabs and slots of the laminae arecharacteristics which may be varied to suit the particular apparatusand/or the stacks it produces.

As in the previously-discussed embodiment, to minimize the risk ofundesirable bowing, the alignment surfaces of choke passageway 272utilize a relatively light interference fit which exerts a reducedpressure on each individual lamina but which develops that pressure overa relatively greater vertical depth to thereby provide an adequate totalback pressure for engagement of the interlock tabs. For example, in anapplication wherein a conventional interference fit might involve a0.001 inch interference fit and a choke depth of 1.25 inches, thepresent application might utilize a 0.0002 to 0.0005 inch interferencefit and a choke depth of 3 inches. Resistance to downward movementwithin the choke is needed to facilitate the engagement of the interlocktabs of the lamina being blanked with the interlock slots of theuppermost lamina in the choke passageway. The pressure exerted on theindividual laminae not only provides resistance to downward motionthrough the choke passageway, but also helps maintain the laminae inproper alignment.

The stacking of one of a plurality of laminae which form a stack 200 isschematically illustrated in FIGS. 26-29, which generally correspond toFIGS. 14-17 discussed above. FIGS. 26-29 sequentially illustrateblanking Station No. VI of FIG. 22, at which an individual lamina 296 isautomatically stacked within choke passageway 272 during a single diestroke. Further, as shown in FIGS. 24 and 25, each of the corners wherechoke side surfaces 278, 280 join upper surface 292 of lower blankingdie bed 294 are provided with lead-in radius 297, which may beapproximately 0.005 to 0.010 inches. Lead-in radii 297 help the widestlaminae enter and become laterally centered in the choke. Notably,lead-in radii are not used on choke surfaces which interact with a punchfor cutting lamina edges.

As described above, the laminae which comprise lamina stack 200 areformed by stamping various features in strip stock material 236 as itprogresses through the die assembly prior to reaching the Station No.VI. The laminae are attached to the strip stock material at theirlongitudinal ends, which are severed by blanking punch 270 to form firstand second end edges 212, 214 thereon. Strip stock material 236 includespilot pin holes 238 which form apertures in the carrier portion of thestrip stock material, i.e., that portion of strip stock material whichis not used to form laminae. Pilot pin holes 238 are used to maintainthe strip stock material in a desired position relative to the diestations as it is stamped during its advancement through the dieassembly. As can be seen in FIGS. 26-29, pilot pin 298 passes throughpilot pin hole 238 and enters guide bore 300 to properly locate stripstock material 236 and the laminae which are attached thereto relativeto the blanking station prior to stamping the strip stock material 236.Although only one pilot pin 298 is illustrated, pilot pins are locatedadjacent each punching station of the die assembly to maintain stripstock material 236 in proper alignment during stamping operations.

FIG. 26 schematically illustrates a portion of upper die assembly 302and lower die bed 294. Upper die assembly 302 reciprocates vertically,together with pilot pin 298 and blanking punch 270, to stamp thelaminae. Blanking punch 270 severs each lamina from the remainder ofstrip stock material 236 and pushes that laminae into engagement withthe uppermost lamina layer disposed in choke passageway 272.

Blanking punch 270 includes staking punch inserts 304 which extend belowthe bottom surface of the blanking punch by a distance designated 306 inFIG. 26. Staking punches 304 correspond to the location of interlocktabs 308 and enter the lamina slot 310 of the lamina being blanked fromstrip stock 236 and positively engage the respective lamina tabs 308 bof the lamina being blanked with the respective interlock slots 310 u ofthe uppermost lamina layer disposed in choke passageway 272.

Staking punch inserts 304 are held in a fixed position relative toblanking punch 270 and each include head 312 which is seated in acounterbore in blanking punch 270. A grind collar (not shown) may belocated below head 312 to permit the lowering of staking punch 304relative to blanking punch 270. Lowering of the staking punch might benecessary due to chipping or wear of staking punch 304 or to accommodatedifferent interlock tab depths. As described above, a number ofdifferent interlock tab designs are known in the art and the tab designwill influence the selection of the appropriate tab depth. In theillustrated embodiment, lamina stack 200 utilizes a design in which noportion of interlock tab 308 is completely severed from the surroundinglamina material. Instead, interlock tab 308 is partially blanked fromthe surrounding material, deforming, but not severing, the material atthe edges of interlock tab 308, and extend below the bottom of theremainder of the lamina by approximately ½ to ⅓ the thickness of thelamina layer. As described above, alternative embodiments of the presentinvention may employ alternative interlock styles or have the interlocktabs extend a greater or less distance below the remainder of thelamina.

The thickness of the lamina is designated 314 in FIG. 26, and isapproximately 0.010 to 0.015 inch, although stacks made according to thepresent invention may comprise thicker laminae. The distance by whichtab 308 extends below the lower lamina surface is designated 316 in FIG.26 and is equivalent to the distance 306 by which staking punch 304extends below blanking punch 270. Because these laminae are rather thin,distance 316 may be equivalent to lamina thickness 314 or even greaterto ensure proper engagement of tab 308 b with mating slot 310 u; thematerial forming tabs 308 will compress slightly towards the undersideof its lamina should distance 316 of tab 308 b be greater than the depthof tab 310 u. Should tabs 308 of lamina 234, which overlies bottommostlamina 220 of a stack extend completely through slots blanked 230 in thebottommost lamina, however, distance 316 should not be so great as topermanently engage the tabs of lamina 234 and slots 310 of topmostlamina 222 of the stack below. The length designations shown in FIG. 26are included merely to provide a convenient mechanism for graphicallyidentifying the lengths and spatial relationships discussed herein andare not necessarily to scale.

As discussed above, staking punches 304 are used to ensure engagement ofinterlock tabs 308 into interlock slots 310 and to prevent interlocktabs 308 from being forced upwardly into the horizontal plane of theremainder of the lamina when tab 308 engages the uppermost lamina inchoke passageway 272. Distance 306 which staking punches 304 extendbelow the bottom surface of blanking punch 270 is equivalent to thedepth it is desired to have interlock tab 308 enter interlock slot 310of the lower adjacent lamina, and generally will be equivalent todistance 316 which interlock tab 308 extends below the lower surface ofstrip stock material 236 when tab 308 is formed.

Each of the laminae of stack 200 has at least one interlock featureformed therein. The bottom lamina of each stack, however, has itsinterlock tabs completely blanked, i.e., removed, to prevent the bottomlamina 220 from being engaged with uppermost lamina 222 of thepreviously formed stack when bottom lamina 220 is separated from thestrip stock material and pushed into the choke passageway. Interlockingtabs 308 and slots 310 of adjacent lamina layers maintains the laminalayers in proper relative alignment both when the stack is within chokepassageway 272 and after the stack has been removed from the chokepassageway.

Stock lifters 318 are used to prevent interlock tabs 308 from beingbiased upwardly into the horizontal plane of the strip stock material236 or from being snagged on lower die bed 294 during the progressivemovement of strip stock material 236. Stock lifters 318 are biasedupwards by springs 320 and lift strip stock material 236 above uppersurface 292 of lower die bed 294 when strip stock material 236 is beingadvanced between die stamping strokes. The strip stock material 236 islifted by stock lifters 318 a distance designated 322 in FIG. 26. Lifterdistance 322 is usually equivalent to approximately 1.5 times thethickness 314 of strip stock material 236 to provide an ample clearance.The illustrated stock lifters 318 are cylindrical, but other types ofstock lifters, such as bar type lifters, are known in the art and canalso be used with the present invention.

FIG. 26 illustrates the relative positions of upper die assembly 302,punches 270, 304, lower die bed 294 and strip stock material 236 at theinitiation of a stamping stroke at the blanking station of the dieassembly (Station No. VI of FIG. 22). FIG. 27 illustrates the dieassembly during the downstroke after pilot pin 298 has extended throughpilot pin hole 238 and has entered guide bore 300 to thereby properlylocate strip stock material 236 and lamina 296 attached thereto. Shortlyafter pilot pin 298 has properly aligned strip stock material 236, andthe laminae attached thereto, staking punches 304 enter the interlockslots 310 of the lamina which is about to be blanked. Shortly afterstaking punches 304 enter interlock slots 310, blanking punch 270engages the upper surface of the lamina.

Stock lifter spring 320 has been compressed and strip stock material 236is pressed against upper surface 292 of lower die bed 294 in FIG. 27.Strip stock material 236 may be pressed against lower die bed 294 byengagement with the downwardly moving punches or by another suitablemechanism, such as a spring stripper, attached to upper die assembly302, which presses the strip stock material against lower die bed 294prior to the engagement of the punches and strip stock material 236.

FIG. 28 illustrates the blanking station after blanking punch 270 hasbegun to sever lamina 296 from the remainder of strip stock material236. As shown schematically in FIG. 28, interlock tabs 308 b of lamina296 are already partially engaged with interlock slots 310 u of theuppermost lamina layer in choke passageway 72. The partial engagement ofinterlock tabs 308 b and interlock slots 310 u occurs prior to thecomplete separation of lamina 296 from the remainder of the strip stockmaterial.

To accomplish the engagement of interlock tabs 308 b and interlock slots310 u of adjacent laminae prior to the complete severing of the blankedlamina layer from the strip stock material 236 the uppermost lamina mustbe positioned in choke passageway 272 near upper surface 292 of lowerdie bed 294. The uppermost lamina is positioned a distance 324 (FIG. 26)below the entrance of choke passageway 272 located in upper surface 292of lower die bed 294.

Distance 324 is determined by the distance blanking punch 270 enterschoke passageway 272 at the end of the die assembly downstroke as shownschematically in FIG. 29. Punch entry distance 324 is typically greaterthan thickness 314 (FIG. 26) of the strip stock material in conventionaldie assemblies. For example, for a strip stock thickness 314 equivalentto 0.015 inch, a conventional die assembly would often have a punchentry between 0.020 and 0.025 inch.

The present invention, however, utilizes a much smaller punch entrywhich ensures that interlock tabs 308 b of blanked lamina 296 areengaged with slots 310 u of the uppermost lamina layer in the chokepassageway prior to completely severing lamina 296 from the remainder ofstrip stock material 236. For example, by utilizing a distance 324 whichis smaller than distance 316 (FIG. 26), tabs 308 b will be partiallyinterlocked with slots 310 u when the die assembly reaches the positionshown in FIG. 27. Alternatively, distance 324 can be equivalent todistance 306 (FIG. 26) as shown in FIGS. 26-29 and interlock tabs 308 bwill be engaged with slots 310 u as lamina 296 being blanked is beingsevered from strip stock material 236 but prior to complete separationas shown in FIG. 29. It may also be possible to have a distance 324slightly larger than distance 306 and still provide for the partialinterlocking of tabs 308 b and slots 310 u prior to complete separationof the lamina layer. The partial interlocking in such an arrangement,however, would be minimal.

Blanking punch 270 severs the longitudinal ends of lamina 296 from theremainder of strip stock material 236 in cooperation with cutting edgeson the upper lip of choke passageway 272, forming first and second endedges 212, 214. Typically, after blanking punch 270 has sheared thelamina to a depth which is approximately ⅓ of the lamina thickness, thelower ⅔ of the strip stock material will fracture and the lamina layerwill be completely separated from the strip stock material. The use of asofter, more elastic strip stock material, however, would permit theblanking punch to enter the strip stock material for more than ⅓ of thelamina thickness and produce a lamina with a smaller fracture zone.

The downstroke is finished by pushing lamina 296 into further engagementwith the uppermost lamina in choke passageway 272 and pushing lamina 296to a depth 324 (FIG. 26) below upper surface 292 of lower die bed 294 asschematically illustrated in FIG. 29. After blanking punch 270 isretracted, stock lifters 318 elevate strip stock material 236, theloose, free end 326 (see FIGS. 22, 29) of which is removed from pin 298and eventually discarded. The remainder of strip stock material 236 isadvanced within the die assembly, and the stamping cycle is repeated.

It should be recognized that although the individual lamina for thestack shown in FIGS. 20 and 21 are rectangular in shape, a structurewith lamina of any shape can be manufactured. For instance, the laminacould have a continuous perimeter without any sharp corners, such asovals or circles. In that case, the choke barrel would contact portionsof the continuous edge. The outer perimeter or edge of a laminationcould be arbitrarily divided into various portions or “edges”. Forpurposes of this description, the word “edge” could therefore mean aportion of a continuous edge, such as a portion of the outer perimeterof a circular or oval shaped lamination.

A die assembly embodying the present invention may be operated at speedswhich are typical for interlocked laminae, e.g., 300 strokes per minute.The maximum speed of operation of any particular die assembly isdependent upon a number of different variables relating to thecomplexity of the die assembly and the material handling requirementsimposed upon the die assembly by the dimensions and configuration of thelamina stack being manufactured. For most lamina stack and die assemblydesigns, however, the stamping and stacking of two discrete laminasegments to form a single layer in a lamina stack should not, by itself,have a direct impact upon the speed at which individual die assembliesare operated.

The ability to automatically stamp and interlock a plurality ofinterlocking laminae into an elongate stack having a cross sectionalshape having sides which do not conform to a plane parallel with thedirection of stack travel through the choke passageway permits theeconomical manufacture of such parts which might otherwise be moreexpensively manufactured by methods employing separate stamping,stacking and interlocking means.

Those skilled in the art will recognize that the above-described methodsand apparatus may be combined to produce elongate stacks having crosssectional shapes having side surfaces formed by lamina side edges whichdo not engage choke passageway and in which the lamina layers arecomprised of a plurality of discrete lamina segments, each segmentprovided with interlocking means.

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains.

What is claimed is:
 1. A die assembly for manufacturing a pencil corecomprising a stack of a plurality of rectangular, elongate, slenderlaminae from strip stock material, said laminae having substantiallyequal lengths, each said lamina having a substantially uniform widththroughout its length, said stack being substantially circular in crosssection and having a widest lamina which is the widest lamina in saidstack, and a plurality of laminae of decreasing widths located bothabove and below said widest lamina, said die assembly comprising: aplurality of punching stations, each punching station having a punch forstamping features in said strip stock material, at least two of suchpunches being selectively actuable, said features defining said elongatelaminae, each said lamina having generally opposite first and secondedges, said features further defining interlock elements adapted toengage another lamina, said laminae connected to a carrier portion ofthe strip stock material; a blanking station comprising a blankingpunch, said blanking punch separating a lamina from the carrier portionof the strip stock material; and an elongate choke cavity disposed belowsaid blanking punch and into which said laminae are received, said chokecavity dimensioned to hold said stack only by said widest lamina.
 2. Thedie assembly of claim 1, wherein said blanking punch includes a lowersurface and at least one staking punch insert extending from said lowersurface.
 3. The die assembly of claim 1, wherein said blanking stationis provided with means for forming one of a notch and a protrusion at anedge of a lamina, said choke cavity provided with one of a notch and aridge to cooperatively engage a corresponding one of said protrusion andnotch provided in each said lamina.
 4. A die assembly for manufacturinga stack of interlocked elongate, slender laminae from strip stockmaterial, said laminae having substantially equal lengths, each saidlaminae having a substantially uniform width throughout its length, saidstack being substantially circular in cross section and having a widestlamina which is the widest lamina in said stack, and a plurality oflaminae of decreasing widths located both above and below said widestlamina, said die assembly comprising: a plurality of punching stations,each punching station having a punch for stamping features in said stripstock material, at least two of such punches being selectively actuable,said features defining elongate laminae each having generally oppositefirst and second edges, said features further defining interlockelements for interlocking said laminae, said laminae connected to acarrier portion of the strip stock material; a strip stock materialalignment member operatively associated with said plurality of punchingstations; a blanking station comprising a blanking punch disposed overan elongate choke cavity for separating a lamina from the carrierportion of the strip stock material; a choke operably associated withsaid blanking station, said choke engaging said stack only by saidwidest lamina; and a lamina securing element to secure at least two ofsaid laminae to each other in said die assembly.